The present invention relates generally to the field of tissue repair and more particularly to composite scaffold implants and scaffold fixation devices with post-type anchors received in a hole formed in underlying tissue.
Porous ceramic materials such as hydroxyapatite, soluble glasses and ceramic forms have been used as scaffolds for the ingrowth of tissue due to compositional and morphological biocompatability. For example, the porosity of such materials promotes cell infiltration. A variety of methods are used to prepare porous ceramic scaffolds (prostheses), such as hydrothermally treating animal bone or coral, burning off polymer beads mixed into a ceramic body, vapor deposition on foam, infiltration of polymer foam with a ceramic slip and foaming a ceramic slip.
One limitation exhibited by porous ceramic materials is their inherent brittleness. Attempts to address this limitation have included back-filling a ceramic foam with monomer solutions of PMMA or PLA, draining excess solution from the ceramic foam then polymerizing through curing and/or drying in order to impart some toughness to the ceramic foam. Others have proposed laminating solid or porous polymeric layers to a ceramic foam structure.
Independent from proposed uses in combination with ceramics, polymeric foams have utility in the repair and regeneration of tissue. For example, amorphous, polymeric foam has been used to fill voids in bone. Various methods have been explored for preparing the polymer foams, using, e.g., leachables; vacuum foaming techniques; precipitated polymer gel masses; and polymer melts with fugitive compounds that sublime at temperatures greater than room temperature. The formation of biocompatible absorbable foams by lyophilization is discussed in a copending patent application entitled xe2x80x9cPorous Tissue Scaffoldings for the Repair and Regeneration of Tissuexe2x80x9d, assigned to Ethicon, Inc., docket number 09/345096, filed Jun. 30, 1999, hereby incorporated by reference.
Hinsch et al. (EP0274898) describes a porous open cell foam of polyhydroxy acids for the in growth of blood vessels and cells. The foam can be reinforced with fibers, yarns, braids, knitted fabrics, scrims and the like.
Athanasiou et al. (U.S. Pat. No. 5,607,474) have proposed using a two-layer polymeric foam device for repairing osteochondral defects at a location where two dissimilar types of tissue are present. The two polymeric layers are prepared separately, and joined together at a subsequent step. Each of the layers is designed to have stiffness and compressibility values that correspond respectively to cartilage and bone tissue, mimicking the cartilage/bone interface. However, the Athanasiou device exhibits an abrupt change in properties from one layer to the next, whereas the juncture of cartilage and bone displays a gradual transition, with cartilage cells gradually changing cell morphology and orientation depending on the location relative to the underlying bone structure. Further, collagen fiber orientation within the matrix also changes relative to its location in the structure.
H. Levene et al., U.S. Pat. No. 6,103,255 describes a process used for making a scaffold having a substantially continuous polymer phase with a distribution of large and small pore sizes, with the small pores contained in the walls of the large pores.
In a study done by G. Niederauer et al. and reported in Biomaterials 21 (2000) 2561, scaffolds for articular cartilage repair were prepared from layers of polylactic/polyglycolic acid (PLG) and polylactic/polyglycolic acid reinforced with fibers of the same material, bioglass or calcium sulfate. The PLG layer was made porous in all cases by expanding a precipitated gel mass of polymer under vacuum at elevated temperatures. The reinforced layers were made porous in a similar fashion after incorporating the reinforcement in the polymer solution and prior to precipitation of the polymeric gel mass. Once the two layers were fabricated, they were adjoined using a small amount of solvent to glue the two layers together.
The use of a porous polymer for the purpose of engineering cartilage is described in the patent by T. Mahood et al. (EP1027897A1) which discloses a multi-layer polymer scaffold in which the layers are attached by successive dip coating or by the attachment of the two layers to a third. The third layer is described as a barrier to cell diffusion, thus confining chondrocytes to the polymer layer and osteoblasts to the ceramic layer.
Kreklau et al. in Biomaterials 20 (1999) 1743 have evaluated a fibrous polymeric fleece attached to a porous ceramic material, for the purpose of culturing chondrocytes in the polymeric scaffold while simultaneously providing a bone formation inducing absorbable material to simulate articular cartilage. In this study, a fibrin-cell-solution was used to affix the ceramic and polymeric layers by way of encapsulation with the intent that the phases would interact in vitro in order to create a mechanically stressable junction. The authors discuss the possibility of providing the surfaces of the layers with teeth to increase shear strength. However, there is no mechanism by which the two different layers are interlocked to resist delaminating forces in directions perpendicular to the laminate function and there is an abrupt transition between the two layers.
In addition to the limitations of the prior art relative to the composition and morphology of tissue scaffolds, the fixation of the scaffold at the site of injury remains challenging. Various fixation methods have been explored, including press-fitting the scaffold into the defect (which may result in slippage or destruction of the implanted scaffold) or suturing the scaffold to the periosteal flaps. The latter approach is not always ideal because the geometry of the scaffold may not match that of the periosteal flaps or the flaps may have been destroyed or cannot be located.
It would therefore be advantageous to overcome the above mentioned limitations with a scaffold that provides secure attachment to a defect site.
The limitations of the prior art are solved by the present invention which includes a prosthetic implant having a tissue scaffold and a fixation device with a scaffold support and an anchoring post. The anchoring post extends from a surface of the scaffold support at a selected angle with the scaffold support embedded within the scaffold.